The invention relates to the formation of semiconductor devices. More specifically, the invention relates to the providing process indicators for etch tools for the formation of semiconductor devices.
During semiconductor wafer processing, features of the semiconductor device are defined in the wafer using well-known patterning and etching processes. In these processes, a photoresist (PR) material is deposited on the wafer and then is exposed to light filtered by a reticle. Thereafter, the wafer is etched to remove the underlying material from the areas that are no longer protected by the photoresist material, and thereby define the desired features in the wafer. Characteristics of features that are typically measured in semiconductor process are CD, etch rate, loading, profile, selectivity, bow, etc. There are many more “specs” that are important in fabrication. CD is an important parameter that is considered, in part because it defines the feature node.
Repeatability for different wafers processed in the same semiconductor processing device and between identical semiconductor processing devices, or even different types of semiconductor process device, is becoming one of the most pertinent issues in the semiconductor industry. Just etching the feature once is not enough, it must be reproducible across the entire wafer, and for every wafer on every tool all the time. Repeatability is important, because a large number, such as trillions, of transistor are etched on each wafer, where a large number of wafers are processed every day. Repeatability includes uniformity (within a wafer), wafer-to-wafer, lot-to-lot, chamber-to-chamber, over-time, even for process transfer between two chambers with different hardware. Achieving such uniform and consistent repeatability is a problem in the industry.
One method used to try to obtain such consistency is to try to get the tool as calibrated and identical as possible between tools or over time. The theory is that if the tool is identical, then the results will be identical. In practice, this helps, but doesn't fully address the problem. For example, a tool might be verified as calibrated, but if there is dirt on the chamber walls, or if a part is worn down, then the results are non-uniform. Blanket etch tests may be used to try to get an idea of how the plasma is working, but these blanket tests do not normally correlate to pattern wafer results, such as CD, which is very important to be able to predict. It is important to know if a chamber is ready to correctly etch an expensive patterned wafer, before the expensive patterned wafer is etched.